Jenson Button already has the title in the bag, according to rival racer Felipe Massa.

Although the 29-year-old Briton will only concede that a sixth win at race No.7 in tomorrow's Turkish Grand Prix will put him on easy street for the rest of the season, Ferrari's Massa believes it would be game over.

The little Brazilian, who battled it out with Lewis Hamilton until the final corner last season, says there will be no repeat from him or anyone else this year.

And he is in a good position to know.

Not just as the man who beat Michael Schumacher around this circuit in the same car and as the winner here for the last three years.

But also as a fellow countryman of Button's biggest championship rival, Rubens Barrichello, sitting across the garage at Brawn.

"I am not the type who gives up easily, I fight to the end," said Massa.

"But I believe Brawn GP will win the championship. It is impossible that Button will give away many points in the coming races. The championship is already over for me, I am too far behind.

"But that doesn't mean I won't be fighting to win every race."

If Button wins here in the sun-baked hills beyond Istanbul, he will have outdone the pace at which Michael Schumacher marched to glory in 2002, his most dominant season, when he won the title by a record margin.

The German legend claimed five of the first six races, was third in the other and second in the seventh. Button has five wins and a third.

With victory tomorrow, the Brit will go one better than the most successful driver in the sport's history. But the man from Frome, Somerset, refuses to accept that the dream he has had since childhood could soon become reality.

A dream just three months ago he thought had died along with his Grand Prix career as his battered team's future hung in the balance.

"If I win on Sunday I will still not believe it is going to be my championship," said Button.

"I will think I have made life easier for myself going forward. I go to every race and think it is not done and dusted, it is not going to be a walk in the park, and it hasn't been.

"I am not pinching myself thinking I have won five races out of six. It is more 'I am six races in, I've won five so let's do the next one'.

"There is no reason to think about the world championship at this stage. We are not even half-way through the season."

Button and Hamilton ended the first day's practice in 12th and 13th place, half a second slower than McLaren pacesetter Heikki Kovalainen.